This invention relates in general to deposition of a metal by electrolytic means on selected regions of a substrate and in particular to pattern generation on anodized aluminum lithographic printing plates by means of laser conditioning of selected regions of the surfaces followed by electrolytic deposition of copper in these regions.
Recording information by the generation, or "writing", of precise patterns on lithographic printing plates is an important step in the production of newspapers and other printed materials. Thus there is considerable interest in developing techniques which reduce the time, material, and labor required to record lithographic printing plate patterns that are wear-resistant and have a long shelf life.
Conventional lithographic recording techniques consist of several steps which include forming a 1:1 negative of a paste up, or original copy, to be printed, developing the negative, vacuum contacting the negative onto a photosensitized plate, and directing light from a mercury vapor or metal halide lamp through the entire negative simultaneously, thereby exposing the photosensitive, coated plate. The plate must then be developed, as by removal of the unexposed photosensitive material. This method requires at least several minutes to complete and is both labor-and materials-intensive. Moreover, the resulting plates may lack the durability needed to print large numbers of copies, and/or the shelf life needed to permit reuse several months following the initial print run.
In certain segments of the printing industry laser imaging techniques have now been found preferable to conventional platemaking processes. A laser can image graphics or text onto either film or directly onto photosensitized plates. When used to expose film, the laser beam can be vector-or raster-scanned over the film, its trajectory controlled and its amplitude modulated by a computer. Such film exposure requires only a low power laser. However, the resultant negative must subsequently be used in a manner similar to that of conventional techniques to expose a photosensitized plate. With higher power lasers, the computercontrolled beam can image graphics or text directly onto a photosensitized plate surface. Direct laser plate imaging systems may include a low power laser scanner, such as a HeNe laser, which reads and electronically stores printed matter from the paste up, and a high power ultraviolet laser writing unit which exposes an ultraviolet photosensitive coating on a lithographic plate in accordance with information stored in a computer. Such direct laser imaging processes save considerable amounts of labor and time and also eliminate costly silver-based films used in conventional and laser-to-film platemaking. However, the high cost of these direct laser platemaking systems, their lower than desired speed of forming patterns on the lithographic plates, and the limited shelf life of plates made using photosensitive materials are drawbacks to these methods. Also, typical printing run lengths achievable with plates formed using laser imaging processes are limited by the durability and wear resistance of the ultraviolet-sensitive, polymeric materials used.
Accordingly, it is a general object of the present invention to provide an improved method of depositing a metal on spatially selected areas of an electrically insulating coated metal substrate.
Another object of the invention is to provide a method of laser-conditioning spatially selected areas of an electrically insulating coating on a metal substrate so that electrolytic processes will deposit metal in these areas.
Particular objects of the invention are to provide a method of producing printing plates whose print features are durable and capable of long print runs and have a long shelf life, and to provide a method of recording on lithographic printing plates which, in addition to the above-stated objects, is more rapid, labor saving, and less material intensive than existing methods.